docs: def depth(self):
          """Depth at grid centers (m)
  
          :getter:    Returns the points of axis ``'depth'`` if availible in the
                      process's domains.
          :type:      array
          :raises: :exc:`ValueError`
                      if no ``'depth'`` axis can be found.
  
          """
          try:
              for domname, dom in self.domains.items():
                  try:
                      thisdepth = dom.axes['depth'].points
                  except:
                      pass
              return thisdepth
          except:
              raise ValueError('Can\'t resolve a depth axis.')